Posterior Prosthetic Intervertebral Disc

ABSTRACT

A prosthetic intervertebral disc is formed of first and second end plates sized and shaped to fit within an intervertebral space and to be implanted from the back of the patient, thereby decreasing the invasiveness of the procedure. The posterior approach provides for a smaller posterior surgical incision and avoids important blood vessels located anterior to the spine particularly for lumbar disc replacements. The first and second plates are each formed of first, second and third parts are arranged in a first configuration in which the parts are axially aligned to form a low profile device appropriate for insertion through the small opening available in the TLIF or PLIF approaches described above. The three parts of both of the plates rotate and translate with respect to one another in situ to a second configuration or a deployed configuration in which the parts are axially unaligned with each other to provide a maximum coverage of the vertebral end plates for a minimum of insertion profile. Upon deployment of the disc, a height of the disc is increased.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.61/081,952 filed Jul. 18, 2008,entitled “POSTERIOR PROSTHETICINTERVERTEBRAL DISC” the full disclosure of which is incorporated hereinby reference.

BACKGROUND OF THE INVENTION

The present invention relates to medical devices and methods. Morespecifically, the invention relates to intervertebral prosthetic discsand methods of preserving limited motion upon removal of anintervertebral disc.

Back pain takes an enormous toll on the health and productivity ofpeople around the world. According to the American Academy of OrthopedicSurgeons, approximately 80 percent of Americans will experience backpain at some time in their life. In the year 2000, approximately 26million visits were made to physicians' offices due to back problems inthe United States. On any one day, it is estimated that 5% of theworking population in America is disabled by back pain.

One common cause of back pain is injury, degeneration and/or dysfunctionof one or more intervertebral discs. Intervertebral discs are the softtissue structures located between each of the thirty-three vertebralbones that make up the vertebral (spinal) column. Essentially, the discsallow the vertebrae to move relative to one another. The vertebralcolumn and discs are vital anatomical structures, in that they form acentral axis that supports the head and torso, allow for movement of theback, and protect the spinal cord, which passes through the vertebrae inproximity to the discs.

Discs often become damaged due to wear and tear or acute injury. Forexample, discs may bulge (herniate), tear, rupture, degenerate or thelike. A bulging disc may press against the spinal cord or a nerveexiting the spinal cord, causing “radicular” pain (pain in one or moreextremities caused by impingement of a nerve root). Degeneration orother damage to a disc may cause a loss of “disc height,” meaning thatthe natural space between two vertebrae decreases. Decreased disc heightmay cause a disc to bulge, facet loads to increase, two vertebrae to rubtogether in an unnatural way and/or increased pressure on certain partsof the vertebrae and/or nerve roots, thus causing pain. In general,chronic and acute damage to intervertebral discs is a common source ofback related pain and loss of mobility.

When one or more damaged intervertebral disc cause a patient pain anddiscomfort, surgery is often required. Traditionally, surgicalprocedures for treating intervertebral discs have involved discectomy(partial or total removal of a disc), with or without interbody fusionof the two vertebrae adjacent to the disc. When the disc is partially orcompletely removed, it is necessary to replace the excised disc materialwith natural bone or artificial support structures to prevent directcontact between hard bony surfaces of adjacent vertebrae. Oftentimes,pins, rods, screws, cages and/or the like are inserted between thevertebrae to act as support structures to hold the vertebrae and anygraft material in place while the bones permanently fuse together.

A more recent alternative to traditional fusion is total discreplacement or TDR. TDR provides the ability to treat disc related painwithout fusion provided by bridging bone, by using a movable,implantable, artificial intervertebral disc (or “disc prosthesis”)between two vertebrae. A number of different artificial intervertebraldiscs are currently being developed. For example, U.S. PatentApplication Publication Nos. 2005/0021146, 2005/0021145, and2006/0025862, which are hereby incorporated by reference in theirentirety, describe artificial intervertebral discs with mobile bearingdesigns. Other examples of intervertebral disc prostheses are the LINK®SB Charité disc (provided by DePuy Spine, Inc.) MOBIDISC® (provided byLDR Medical (www.ldrmedical.fr)), the BRYAN Cervical Disc (provided byMedtronic Sofamor Danek, Inc.), the PRODISC® or PRODISC-C® (from SynthesStratec, Inc.), the PCM disc (provided by Cervitech, Inc.), and theMAVERICK® disc (provided by Medtronic Sofomor Danek).

A potential drawback of these known disc designs is that the prostheticdisc must be inserted from the anterior side of the patient. Theanterior approach can be difficult and may require a vascular surgeon asthe prosthetic disc passes near important blood vessels located anteriorto the spine. Other currently available intervertebral disc prosthesesusually have similar drawbacks, including invasiveness of the surgeryand/or surgical skill and complexity.

Another prosthetic approach has been to fuse the vertebrae, for examplewith transforaminal lumbar interbody fusion (TLIF) surgery or posteriorlumbar interbody fusion (PLIF) surgery. These procedures allow thesurgery to be performed from the posterior without passing through theabdominal cavity and the associated drawbacks. The TLIF or PLIFapproaches involve passing through a much smaller space than an anteriorapproach and generally require at least partial removal of one or morefacet joints to provide enough space for access to the disc space. It isthis limitation on space that has until now prevented the design of asuccessful artificial disc for delivery by a TLIF or PLIF approach.

Therefore, a need exists for an improved disc for preserving motion andmaintaining disc spacing between two vertebrae after removal of anintervertebral disc which can be delivered by a TLIF or PLIF approach.Ideally, such improved disc would be introduced in a small configurationand expanded in vivo to a larger configuration.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention provide a prosthetic intervertebraldisc which is implanted from a PLIF or TLIF approach and is deployedfrom a small insertion configuration to a larger deployed configurationin vivo.

In accordance with one aspect of the invention, a prostheticintervertebral disc includes first and second end plates sized andshaped to fit within an intervertebral space, each end plate having avertebral contacting surface and an inner surface and a first bearingsurface on an inner surface of the first end plate and a second bearingsurface on an inner surface of the second end plate. The first andsecond bearing surfaces are arranged to allow articulation and rotationbetween the first and second plates. The first and second plates areeach formed of first, second and third parts having a firstconfiguration in which the parts are axially aligned to a secondconfiguration in which the parts are axially unaligned with each other.The first and second plates are deployed in situ from the firstconfiguration to the second configuration by both rotation and slidingof the parts over one another. The deployment from the firstconfiguration to the second configuration increases a height of thedisc.

In accordance with another embodiment of the invention, a prostheticintervertebral disc includes first and second end plates sized andshaped to fit within an intervertebral space, each end plate having avertebral contacting surface and an inner surface, a first bearingsurface on an inner surface of the first end plate and a second bearingsurface on an inner surface of the second end plate, the first andsecond bearing surfaces opposed to one another, and a mobile coreconfigured to be received between the first and second bearing surfacesand arranged to allow articulation and rotation between the first andsecond plates. The first and second plates are each formed of first,second and third parts having a first configuration in which the partsare axially aligned and a second configuration in which the parts areaxially unaligned with each other. A track is formed in the first andsecond end plates. The track is configured to allow the mobile core tomove from a first position outside of the bearing surfaces to a positionbetween the bearing surfaces, wherein the movement of the mobile corefrom the first position to the second position increases a height of thedisc.

In accordance with a further aspect of the invention, a method ofdeploying a prosthetic intervertebral disc comprises the steps of:providing a prosthetic intervertebral disc having first and second endplates each having a vertebral contacting surface and an inner surface,a first bearing surface on an inner surface of the first end plate and asecond bearing surface on an inner surface of the second end plate, thefirst and second bearing surfaces arranged to allow articulation androtation between the first and second plates, wherein the first andsecond plates are each formed of first, second and third parts;inserting the intervertebral disc between two vertebrae in aconfiguration in which the first, second and third parts of each of theplates are axially aligned; and deploying the first and second plates insitu from the first configuration to a second configuration in which theparts are axially unaligned with each other by both rotation and slidingof the parts over one another, wherein the deployment from the firstconfiguration to the second configuration increases a height of thedisc. In accordance with an additional aspect of the invention, a methodof deploying a prosthetic intervertebral disc includes the steps of:providing a prosthetic intervertebral disc comprising first and secondend plates and a mobile core arranged to allow articulation and rotationbetween the first and second plates, wherein the first and second platesare each formed of first, second and third parts; inserting theintervertebral disc between two vertebrae in a configuration in whichthe first, second and third parts of each of the plates aresubstantially axially aligned; deploying the first and second plates insitu from the first configuration to a second configuration in which theparts are axially unaligned with each other; and moving the mobile corealong a track between the end plates, wherein the movement of the mobilecore from the first position to the second position increases a heightof the disc.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a posterior prosthetic intervertebraldisc in a narrow insertion configuration;

FIG. 2 is a side view of the disc of FIG. 1;

FIG. 3 is a top view of the disc of FIG. 1;

FIG. 4 is a side cross sectional view of the disc of FIG. 1 taken alongthe line 4-4 of FIG. 3;

FIG. 5 is a cross sectional view of the disc of FIG. 1 taken along theline 5-5 of FIG. 2;

FIG. 6 is a perspective view of the disc of FIG. 1 is an expandeddeployed configuration;

FIG. 7 is a top view of the deployed disc of FIG. 6;

FIG. 8 is a top view of an alternative embodiment of a posteriorprosthetic intervertebral disc in a partially deployed configuration;

FIG. 9 is a perspective view of the disc of FIG. 8;

FIG. 10 is a side view of the disc of FIG. 8;

FIG. 11 is a perspective view of the disc of FIG. 8 with the core movingalong a track from the position of FIG. 8 to the fully deployed positionof FIG. 12; and

FIG. 12 is a perspective view of the disc of FIG. 8 with the core in afully deployed position.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides an implanted intervertebral disc assemblywhich both restores motion and can be implanted from the back of thepatient, thereby decreasing the invasiveness of the procedure. Theposterior approach provides for a smaller posterior surgical incisionand avoids important blood vessels located anterior to the spineparticularly for lumbar disc replacements. The intervertebral discsdescribed herein are designed to be suitable for either a PLIF or TLIFapproach to the spine. These approaches require insertion of a devicewith a small insertion profile which can be expanded or assembled invivo into a complete disc assembly.

PLIF stands for Posterior Lumbar Interbody Fusion. In the PLIF approachto the spine, the vertebrae are reached through an incision in thepatient's back (posterior). The PLIF procedure involves forming a 3-6inch incision in the patient's back and retracting the spinal muscles toallow access to the vertebral disc. The surgeon then carefully removesthe lamina (laminectomy) to be able to see and access the nerve roots.The facet joints, which lie directly over the nerve roots, may betrimmed to allow more room for the nerve roots. Depending on the amountof space available, ¼ to ½ of the facets may be removed. The surgeonthen removes some or all of the affected disc and surrounding tissue.Once the disc space is prepared, hardware, such as an intervertebraldisc, is inserted into the disc space. The space available for insertionof the intervertebral disc can vary depending on the patient, butgenerally the opening has a width and height of about 1 cm which withdistraction can form a slightly larger opening.

TLIF stands for Transforaminal Lumbar Interbody Fusion. The TLIF hasrecently gained popularity as a surgical access to the lumbar spine andprovides some potential advantages over the PLIF approach. The TLIFtechnique involves approaching the spine in a similar manner as the PLIFapproach but more from the side of the spinal canal through a midlineincision in the patient's back. This approach greatly reduces the amountof surgical muscle dissection and minimizes the nerve manipulationrequired to access the vertebrae, discs and nerves. The TLIF approach isgenerally less traumatic to the spine, is safer for the nerves, andallows for minimal access. However, the TLIF involves the removal of atleast one and possibly both facets.

FIG. 1 illustrates a prosthetic intervertebral disc 10 formed of firstand second end plates 12, 14 sized and shaped to fit within anintervertebral space. Each plate 12, 14 has a vertebral contacting outersurface 16 and an inner surface carrying first and second bearingsurfaces 18, 20 (shown in FIGS. 4 and 5). The first bearing surface 18in the embodiment of FIG. 1 is a concave bearing surface while thesecond bearing surface 20 is a mating convex bearing surface. Togetherthe bearing surfaces 18, 20 form a ball and socket joint arranged toallow articulation and rotation between the first and second plates 12,14.

The first and second plates 12, 14 are each formed of first, second andthird parts 22, 24, 26. The three parts 22, 24, 26 have a firstconfiguration, shown in FIG. 1 in which the parts are axially aligned toform a low profile device appropriate for insertion through the smallopening available in the TLIF or PLIF approaches described above.Preferably, the undeployed configuration of FIG. 1 has a height lessthan about 10 mm and a width less than about 12 mm. The three parts 22,24, 26 of both of the plates 12, 14 rotate and translate with respect toone another in situ to a second configuration or a deployedconfiguration in which the parts are axially unaligned with each other.In the deployed configuration, as shown in FIGS. 6 and 7, the threeparts form a substantially H-shaped configuration which provides amaximum coverage of the vertebral end plates for a minimum of insertionprofile. As the three parts 22, 24, 26 translate with respect to oneanother to the deployed configuration a height of the disc is increasedin a manner which will be described in detail below.

The bone integration surfaces 16 of the disc 10 have been shown as flatsurfaces for ease of illustration. The outer vertebral body contactingsurface 16 may take on any of the configurations known in the art.Oftentimes, the outer surfaces 16 will include one or more surfacefeatures and/or materials to enhance attachment of the disc 10 tovertebral bone. For example, the outer surfaces 16 may be machined tohave serrations, teeth or other surface features for promoting adhesionof the plates 12, 14 to a vertebra. In one embodiment, serrations areprovided on the outer surfaces 16. The serrations can be pyramid shapedserrations extending in mutually orthogonal directions, but othergeometries of serrations or other features including teeth, grooves,ridges, pins, barbs and combinations thereof would also be useful. Whenthe bone integration structures are ridges, teeth, barbs or similarstructures, they may be angled to ease insertion and prevent migration.The outer surfaces may include other fixation means inserted afterdeployment of the disc 10, including one or more fins, pins, or screws.In one embodiment, one or more fins are provided on the last of thethree parts to enter the disc space. Optionally, additional fins may beprovided that are inserted after the disc is positioned by sliding thefin(s) into one or more slots in the endplates.

The outer surfaces 16 may be provided with a rough microfinish formed byblasting with aluminum oxide microparticles or the like to improve boneintegration. In some embodiments, the outer surface 16 may also betitanium plasma sprayed or HA coated to further enhance attachment ofthe outer surface to vertebral bone.

The disc 10 may be deployed with the aid of various instrumentsincluding one or more distracters, sizing guides, placement instrumentsand deployment instruments. The deployment instruments can be fixed tothe ends of the disc 10 in the insertion configuration shown in FIG. 1by a connection means, such as a quick connect or a threaded coupling.The placement and deployment instruments generally include at least twoinstruments with one instrument inserted though each of the two openingsformed at the posterior side of the disc space on either side of thespine. Referring now to FIG. 3, the sequence of deployment of the disc10 includes rotation of the first and third parts 22, 26 with respect tothe second part 24 in the direction of the arrows A, followed by slidingof the second part 24 along first and third parts in the direction ofthe arrow B to form the deployed configuration shown in FIGS. 6 and 7.

The disc 10 includes cylindrical pegs 30 on opposite ends of the secondparts 24 which fit into channels 32 on the first and third parts 22, 26to allow first rotation and then translation of the second part alongthe first and third parts. The rotation of the disc 10 from thesubstantially linear arrangement of FIGS. 1-3 to a substantiallyU-shaped arrangement (not shown) can be caused by contact of a leadingend of the inserted disc with an annulus of the natural disc. TheU-shaped configuration is then converted to the final H-shapedconfiguration by pulling the second part 24 posteriorly in the directionof the arrow B. The sliding of the second or center part 24 along thechannels 32 causes the disc space to be distracted, i.e. the height ofthe disc increases from an initial height H_(i), shown in FIG. 2 to adeployed height H_(d), shown in FIG. 6. This distraction or separationof the end plates is provided by ramps 34 which lie along each side ofthe channel 32 in the first and third parts 22, 26. The deployed heightH_(d) is preferably between 1.3 and 2 times the initial height H_(i). Inone example, the deployed height H_(d) is about 1.5 times the initialheight H_(i) and provides a final deployed disc configuration shown inFIG. 6 which is significantly higher than the height of the accessopening provided by the posterior PLIF or TLIF approach.

Another embodiment of a posterior prosthetic intervertebral disc 100 isshown in FIGS. 8-12. The prosthetic disc 100 includes first and secondend plates 112, 114 sized and shaped to fit within an intervertebralspace, each end plate having a vertebral contacting surface 116 and anopposite inner surface including a bearing surface 118. The disc 100includes a mobile core 120 which in a deployed configuration ispositioned between the opposing bearing surfaces 118 to provide a mobilecore articulating disc design. As in the embodiment of FIG. 1, each ofthe plates 12, 114 are formed of first, second and third parts 122, 124,126. The three parts of the plates have a first configuration forinsertion of the disc 100 through a small posterior keyhole into thedisc space. In the first configuration (not shown) the three parts 122,124, 126 are substantially axially aligned. The after insertion, thethree parts 122, 124, 126 are rotated by pivoting on interconnectingposts 130 to a second configuration in which the parts are axiallyunaligned with each other and arranged with the first and third parts122, 126 at an angle of about 20-90 degrees with respect to one another,preferably about 70-85 degrees.

The mobile core 120 includes opposite convex bearing surfaces arrangedto be received between the first and second bearing surfaces 118 of theplates to allow articulation, rotation and some translation between thefirst and second plates. As shown in FIGS. 8-10, for insertion of thedisc 100 into the disc space, the core 120 is positioned in a seat 132formed between the first parts 122 at one end of the first parts. Afterinsertion of the disc 100 into the disc space, the core 120 is advancedalong a track 134, shown in FIG. 11 from the seat 132 to a finaldeployed position between the bearing surfaces 118 of the plates. FIG.12 shows the core 120 seated between the bearing surfaces 118. Thebearing surfaces 118 may include one or more core retaining features,such as a retaining ring or other peripheral retaining features. As canbe seen in FIG. 11, the movement of the mobile core 130 from the firstposition in the seat 132 to the second position between the bearingsurfaces 118 distracts the plates 112, 114 away from one another andincreases a height of the disc 100 from an initial height H_(i), shownin FIG. 10 to a deployed height H_(d) shown in FIG. 12.

The procedure for replacing a natural intervertebral disc with theartificial intervertebral discs 10, 100 includes using a PLIF or TLIFapproach to the spine, by forming a 3-6 inch incision in the patient'sback and retracting the spinal muscles to allow access to the vertebraldisc. The surgeon then carefully removes the lamina (laminectomy) to beable to see and access the nerve roots. The disc space is then enteredthrough a preexisting opening or through an opening formed by cuttingaway a portion of or an entire one or more facet. Those skilled in theart will understand the procedure of preparing the disc space andimplanting the disc which is summarized herein. A far posterio-lateralminimally invasive approach can be used so as to allow for the minimumof facet removal such that the facet joints remain substantially intact.The surgeon then removes some or all of the affected disc andsurrounding tissue. Once the disc space is prepared the intervertebraldisc is inserted into the disc space in the insertion configuration inwhich the first, second and third parts are aligned. The space availablefor insertion of the intervertebral disc can vary depending on thepatient, but generally the opening has a width and height of about 1 cmwhich with distraction can form a slightly larger opening, i.e. about 1cm by 1.2 cm. The deployment of the discs 10, 100 can be performedthrough a single posterior opening, or preferably, through two posterioropenings to allow the surgeon better access to deploy the disc. In oneembodiment, one of the two openings is used for insertion of the discwhile the other opening is used for a distraction instrument and/orother deployment instruments.

The upper and lower plates 12, 14, 112, 114 may be constructed from anysuitable metal, alloy or combination of metals or alloys, such as butnot limited to cobalt chrome alloys, titanium (such as grade 5titanium), titanium based alloys, tantalum, nickel titanium alloys,stainless steel, and/or the like. They may also be formed of ceramics,biologically compatible polymers including PEEK, UHMWPE, PLA or fiberreinforced polymers. The plates 12, 14, 112, 114 may be formed of a onepiece construction or may be formed of more than one piece, such asdifferent materials coupled together.

The core 130 can be made of low friction materials, such as titanium,titanium nitrides, other titanium based alloys, tantalum, nickeltitanium alloys, stainless steel, cobalt chrome alloys, ceramics, orbiologically compatible polymer materials including PEEK, UHMWPE, PLA orfiber reinforced polymers. High friction coating materials can also beused.

Different materials may be used for different parts of the disc 10 tooptimize imaging characteristics. PEEK plates may also be coated withtitanium plasma spray or provided with titanium screens for improvedbone integration. Other materials and coatings can also be used such astitanium coated with titanium nitride, aluminum oxide blasting, HA(hydroxylapatite) coating, micro HA coating, and/or bone integrationpromoting coatings. Any other suitable metals or combinations of metalsmay be used as well as ceramic or polymer materials, and combinationsthereof. Any suitable technique may be used to couple materialstogether, such as snap fitting, slip fitting, lamination, interferencefitting, use of adhesives, welding and the like.

Although the present invention has been described as having a ball insocket design (disc 10) or a mobile core design (disc 100), thearticulation surfaces may be varied to take on any of the differentarticulation designs known in the art. For example, the disc 10 may usea mobile bearing design in place of the ball and socket articulation. Inone alternative embodiment of the invention non-symmetrically shapedbearing surfaces are used to tailor the articulation of the disc to theanatomy. In one example, the bearing surfaces are arranged to allow amaximum of 12 degrees of motion in flexion, a maximum of 8 degrees inextension and a maximum of 8 degrees in each direction of lateralbending. This configuration is useful particularly in the lumbar spinewhere the average range of motion of the various segments is larger inflexion that in extension or lateral bending.

Although the core 130 of FIG. 8 has been shown as circular in crosssection with spherically shaped bearing surfaces, other shapes may beused including oval, elliptical, or kidney bean shaped. The circularshaped core does not limit rotational motion between the plates. Thenon-circular shaped cores can be used to limit rotational motion betweenthe upper and lower plates 112, 113. When the core 130 is formed of apolymer such as PEEK which is invisible under radiographic imaging, itmay be desirable to have a radiographic marker imbedded within the core.

While the exemplary embodiments have been described in some detail, byway of example and for clarity of understanding, those of skill in theart will recognize that a variety of modifications, adaptations, andchanges may be employed. Hence, the scope of the present inventionshould be limited solely by the appended claims.

1. A prosthetic intervertebral disc comprising: first and second endplates sized and shaped to fit within an intervertebral space, each endplate having a vertebral contacting surface and an inner surface; afirst bearing surface on an inner surface of the first end plate and asecond bearing surface on an inner surface of the second end plate, thefirst and second bearing surfaces arranged to allow articulation androtation between the first and second plates; wherein the first andsecond plates are each formed of first, second and third parts having afirst configuration in which the parts are axially aligned and a secondconfiguration in which the parts are axially unaligned with each other,the first and second plates deployed in situ from the firstconfiguration to the second configuration by both rotation and slidingof the parts over one another, and wherein the deployment from the firstconfiguration to the second configuration increases a height of thedisc.
 2. The disc of claim 1, wherein the first, second and third partsare arranged with the second part interconnecting the first and thirdparts.
 3. The disc of claim 2, wherein opposite ends of the second partare arranged to slide along the first and third parts during deployment.4. The disc of claim 3, wherein the opposite ends of the second partslide in elongated tracks on the second and third parts to increase theheight of the disc in a direction perpendicular to the direction ofsliding.
 5. The disc of claim 1, wherein the first bearing surface andthe second bearing surface comprise a ball and socket articulatingjoint.
 6. The disc of claim 1, wherein the first bearing surface and thesecond bearing surface comprise three piece a mobile core articulatingjoint.
 7. The disc of claim 1, wherein first configuration comprises asubstantially linear arrangement.
 8. The disc of claim 7, wherein thesecond configuration comprises a substantially H-shaped arrangement. 9.The disc of claim 7, wherein the disc in the first configuration has aheight and width of less than 12 mm.
 10. A prosthetic intervertebraldisc comprising: first and second end plates sized and shaped to fitwithin an intervertebral space, each end plate having a vertebralcontacting surface and an inner surface; a first bearing surface on aninner surface of the first end plate and a second bearing surface on aninner surface of the second end plate, the first and second bearingsurfaces opposed to one another; wherein the first and second plates areeach formed of first, second and third parts having a firstconfiguration in which the parts are substantially axially aligned and asecond configuration in which the parts are axially unaligned with eachother; a mobile core configured to be received between the first andsecond bearing surfaces and arranged to allow articulation and rotationbetween the first and second plates; and a track formed in the first andsecond end plates, the track configured to allow the mobile core to movefrom a first position outside of the bearing surfaces to a positionbetween the bearing surfaces, wherein the movement of the mobile corefrom the first position to the second position increases a height of thedisc.
 11. The disc of claim 10, wherein the first, second and thirdparts are arranged with the second part interconnecting the first andthird parts.
 12. The disc of claim 11, wherein the first and third partsare arranged to pivot on opposite ends of the second part duringdeployment.
 13. The disc of claim 10, wherein first configurationcomprises a substantially linear arrangement.
 14. The disc of claim 13,wherein the second configuration comprises a substantially H-shapedarrangement.
 15. The disc of claim 10, wherein the disc in the firstconfiguration has a height and width of less than 12 mm.
 16. The disc ofclaim 12, wherein the disc in the second configuration has a height ofat least 1.5 times a height in the first configuration.
 17. The disc ofclaim 1, wherein the disc in the second configuration has a height of atleast 1.5 times a height in the first configuration.
 18. A method ofdeploying a prosthetic intervertebral disc, the method comprising:providing a prosthetic intervertebral disc having first and second endplates each having a vertebral contacting surface and an inner surface,a first bearing surface on an inner surface of the first end plate and asecond bearing surface on an inner surface of the second end plate, thefirst and second bearing surfaces arranged to allow articulation androtation between the first and second plates, wherein the first andsecond plates are each formed of first, second and third parts;inserting the intervertebral disc between two vertebrae in aconfiguration in which the first, second and third parts of each of theplates are axially aligned; and deploying the first and second plates insitu from the first configuration to a second configuration in which theparts are axially unaligned with each other by both rotation and slidingof the parts over one another, wherein the deployment from the firstconfiguration to the second configuration increases a height of thedisc.
 19. The method of claim 18, wherein the first, second and thirdparts are arranged with the second part interconnecting the first andthird parts.
 20. The method of claim 19, wherein opposite ends of thesecond part slide along the first and third parts during deployment. 21.The method of claim 20, wherein the opposite ends of the second partslide in elongated tracks on the second and third parts to increase theheight of the disc in a direction perpendicular to the direction ofsliding.
 22. A method of deploying a prosthetic intervertebral disc, themethod comprising: providing a prosthetic intervertebral disc comprisingfirst and second end plates and a mobile core arranged to allowarticulation and rotation between the first and second plates, whereinthe first and second plates are each formed of first, second and thirdparts; inserting the intervertebral disc between two vertebrae in aconfiguration in which the first, second and third parts of each of theplates are substantially axially aligned; deploying the first and secondplates in situ from the first configuration to a second configuration inwhich the parts are axially unaligned with each other; and moving themobile core along a track between the end plates, wherein the movementof the mobile core from the first position to the second positionincreases a height of the disc.
 23. The method of claim 22, wherein thetrack is formed in inner surfaces of the first and second end plates andis configured to allow the mobile core to move from a first positionoutside of bearing surfaces of the end plates to a position between thebearing surfaces of the end plates.
 24. The method of claim 22, whereinthe second configuration comprises a substantially H-shaped arrangement.25. The method of claim 22, wherein the disc in the first configurationhas a height and width of less than 12 mm.
 26. The method of claim 22,wherein the disc in the second configuration has a height of at least1.5 times a height in the first configuration.